Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MICROWAVES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32Linked to original sources
PubMed2005

Destruction and injury of Escherichia coli during microwave heating under vacuum.

AIMS: To study the effect of 2450 MHz microwave radiation under vacuum (vacuum microwave or VM) on survival and injury of Escherichia coli and to search for possible nonthermal effects associated with VM. METHODS AND RESULTS: Destruction kinetics of E. coli in peptone water were determined in a continuous-flow vacuum system, heated by convection heating in a water bath or with microwaves (VMs). Vacuum was used to control the boiling point of water and to maintain temperature in the bacterial suspensions at specified levels (49-64 degrees C). CONCLUSIONS: z-Value in the water bath treatment was 9.1 degrees C while for VM at 510 and 711 W it was 6.2 and 5.9 degrees C, suggesting that E. coli is more sensitive to temperature changes under microwave heating. Arrhenius calculations of the activation energies of the destruction reactions suggest that the mechanism of destruction in VM may be different from that of conventional heat. The number of injured micro-organisms showed no significant differences among treatments. SIGNIFICANCE AND IMPACT OF THE STUDY: The impact of temperature on E. coli destruction was different when microwaves were the medium of heat transfer, suggesting the existence of factors other than heat contributing to the lethal effect of VM.

Escherichia coli↗
PubMed1992

An improved cryofixation method: cryoquenching of small tissue blocks during microwave irradiation.

The metal contact method of rapid freezing is greatly improved by irradiating the specimen with microwaves at 2.45 GHz for a short period of time (50 ms), while pushing the specimen onto the surface of the copper block cooled by liquid N2. The microwave irradiation, together with two technical improvements (a light-mass plunger and a recently developed beta-gel shock absorber) for preventing bounce, produces a good freezing zone for squid retina, with high reproducibility for each experimental trial, extending from the contact surface to a depth of about 15 microns, which is comparable to the depth obtained by the metal contact method using liquid He in the absence of microwave irradiation. A good freezing zone was also experimentally demonstrated in specimens of rat liver and heart muscle. Microwave irradiation does not have appreciable effects on the ultrastructure of squid retina. The mechanism underlying the improvement in the rapid freezing under the microwave irradiation is discussed.

Animals↗
PubMed1993

Microwave sterilization of polyethylene catheters for intermittent self-catheterization.

A standard household 650 W microwave oven was used to sterilize polyethylene catheters of the type used for intermittent self-catheterization. The catheters were infected with Proteus sp. bacteria and microwaved at 650 W for periods of 2, 4, 6 and 8 minutes. The effect of microwaving was assessed by determining the resultant colony counts following catheter culture. It was determined that 6 minutes of microwaving were required to achieve sterility. It is suggested that use of a microwave oven is a reliable and cost-effective method of sterilizing polyethylene catheters for intermittent self-catheterization.

Catheterization↗
PubMed1987

Low-level microwave irradiations affect central cholinergic activity in the rat.

Sodium-dependent high-affinity choline uptake was measured in various regions of the brains of rats irradiated for 45 min with either pulsed or continuous-wave low-level microwaves (2,450 MHz; power density, 1 mW/cm2; average whole-body specific absorption rate, 0.6 W/kg). Pulsed microwave irradiation (2-microseconds pulses, 500 pulses/s) decreased choline uptake in the hippocampus and frontal cortex but had no significant effect on the hypothalamus, striatum, and inferior colliculus. Pretreatment with a narcotic antagonist (naloxone or naltrexone; 1 mg/kg i.p.) blocked the effect of pulsed microwaves on hippocampal choline uptake but did not significantly alter the effect on the frontal cortex. Irradiation with continuous-wave microwaves did not significantly affect choline uptake in the hippocampus, striatum, and hypothalamus but decreased the uptake in the frontal cortex. The effect on the frontal cortex was not altered by pretreatment with narcotic antagonist. These data suggest that exposure to low-level pulsed or continuous-wave microwaves leads to changes in cholinergic functions in the brain.

Animals↗
PubMed2005

Color stability of dry earth pigmented maxillofacial silicone A-2186 subjected to microwave energy exposure.

PURPOSE: The purpose of this study was to measure spectrophotometrically the color stability of pigmented A-2186 silicone maxillofacial elastomer with 10% by volume of titanium white dry earth opacifier before and after exposure to microwave energy over a simulated 1.5-year period of microwave sterilization. MATERIALS AND METHODS: A-2186 silicone elastomer opacified with titanium white dry earth pigment, pigmented with 5 cosmetic dry earth pigment colors [no pigment (control) group (Pc), red (Pr), yellow ochre (Py), burnt sienna (Po), and a mixture of Pr + Py + Po color group (P3)], was used in this study. Each of the 5 experimental groups consisted of 5 specimens. All specimens were placed in a 250 ml glass beaker filled with 150 ml of water (replenished for each microwave exposure). An exposure of 6 minutes was used 18 times (simulating 1.5 years of microwave sterilization with one 6 minute exposure monthly). Reflectance values were measured by spectrophotometer. Three- and two-way analyses of variance with repeated measures were performed for the color difference (DeltaE*) with the factors of group/color/months, and group/months, respectively. Means were compared by Tukey Honest Significant Difference (HSD) multiple range test calculated at the 0.05 level of significance using SPSS. RESULTS: The trained human eye can detect color changes (DeltaE*) greater than 1.0. Most DeltaE* values of the red pigment group at all intervals and the mixed pigment group at 15- and 18- month intervals increased significantly greater than 1.0 (p < 0.001) compared with the control group. Yellow and burnt sienna groups remained the most color stable over time with DeltaE* values below 0.35. CONCLUSIONS: Lack of color stability of red dry earth pigmented A-2186 silicone maxillofacial elastomers was clinically significant after 12-month exposure to microwave energy as compared with yellow, burnt sienna, and opacified A-2186 dry earth pigments.

Analysis of Variance↗
PubMed1994

Immunohistochemical detection of progesterone receptors in paraffin sections. A novel method using microwave oven pretreatment.

The benefits of microwave oven pretreatment of formalin-fixed routinely processed paraffin sections were assessed using citric acid solution to demonstrate progesterone receptors (PR). Parallel frozen and paraffin sections from 25 cases of breast cancer were stained with the PR-ICA kit (Abbott). Compared with untreated paraffin sections a great enhancement of PR immunostaining occurred after microwave irradiation. In 21 cases the percentage of positively stained tumor cell nuclei in microwave oven-pretreated paraffin sections was practically identical to that in the frozen ones. After microwave irradiation the PR score in paraffin sections was in three cases higher than in the frozen material. In comparison with the frozen sections, only one tumor of 25 showed a lower percentage of stained malignant cells after the irradiation. It is concluded that microwave oven pretreatment is a simple, reliable and reproducible method to detect PR in routinely fixed paraffin-embedded tissues.

Adenocarcinoma↗
PubMed1989

Kinetics of rapid 45Ca uptake into chick skeleton in vivo: effects of microwave fixation.

We have investigated uptake kinetics for 45Ca labels acutely administered as single intravenous injections into twelve-day-old chicks in vivo. Effects of microwave fixation on this process have also been studied. Rapid uptake of 45Ca was demonstrated into the skeleton with approximately 40% of injected label being found in the skeleton within the first 15 min. By 45 min tissue 45Ca levels had stabilized and showed little change during the following 90 min. Soft tissue isotope levels declined during the period from 3 to 135 min following injection. These data were obtained from animals in which tissue isotope levels were stabilized by fixation with microwaves at the point of killing by cervical dislocation. In animals where the microwave fixation step was omitted and tissues were dissected for counting at least 1 h after killing, 45Ca levels in both skeletal and soft tissues were 15-20% higher than in those from microwave groups during the period 3-15 min after injection. In a separate experiment, groups of chicks killed by cervical dislocation 3 min after isotope injection were fixed with microwaves at time intervals ranging from 0 to 45 min post-mortem. Isotope levels in femur increased with time and were significantly higher in groups in which fixation was carried out 12 and 45 min after death when compared with those fixed at the point of death. Data in calvarium reflected those in femur but were not statistically significant at the time intervals tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Microwave tomography for detection/imaging of myocardial infarction. I. Excised canine hearts.

We have demonstrated previously that the dielectric properties of myocardium at microwave spectrum are a sensitive indicator of its blood content, ischemia, and infarction. The purpose of this study is to validate the feasibility of microwave tomography for detection of myocardial infarction based on the differences in dielectric properties between normal and infarcted tissues. Excised canine heats with two weeks myocardial infarction were imaged. Tomographic imaging experiments were conducted using a three-dimensional (3D) microwave tomographic system operating at a frequency of 1.0 GHz. To obtain the images, we used 3D reconstruction algorithms. Images of excised canine hearts with myocardial infarction were obtained at a frequency of 1 GHz, applicable for whole body imaging. Microwave tomographic images were compared with anatomical slices. The comparison confirms that microwave tomography is capable of detection of myocardial infarction.

Animals↗
PubMed2001

Scanning microwave-induced thermoacoustic tomography: signal, resolution, and contrast.

Scanning thermoacoustic tomography was explored in the microwave region of the electromagnetic spectrum. Short microwave pulses were used to induce acoustic waves by thermoelastic expansion in biological tissues. Cross sections of tissue samples were imaged by a linear scan of the samples while a focused ultrasonic transducer detected the time-resolved thermoacoustic signals. Based on the microwave-absorption properties of normal and cancerous breast tissues, the piezoelectric signals in response to the thermoacoustic contrast were investigated over a wide range of electromagnetic frequencies and depths of tumor locations. The axial resolution is related to the temporal profile of the microwave pulses and to the impulse response of the ultrasonic transducer. The lateral resolution is related to the numerical aperture of the ultrasonic transducer as well as to the frequency spectra of the piezoelectric signals in the time window corresponding to the axial resolution. Gain compensation, counteracting the microwave attenuation, was applied to enhance the image contrast.

Acoustics↗
PubMed2005

Ultrasound-guided microwave imaging of breast cancer: tissue phantom and pilot clinical experiments.

Microwave imaging promises high contrast between tumor and normal breast tissues, but its spatial resolution is limited. Here, we present a multimodality approach for high-resolution microwave imaging, where microwave image reconstruction is structurally guided by ultrasound imaging. The combined imaging concept is demonstrated using tissue phantom measurements obtained from a 16 x 15 transmitter/receiver microwave imaging system and a modified B-mode ultrasound system. With the geometry of the target and background known a priori from ultrasound, successful dielectric property images are recovered using a finite element-based reconstruction algorithm. We show that a target as small as 1.2 mm in diameter can be imaged with the multimodality approach, whereas it is impossible to detect such a small-size object using microwave imaging alone. The pilot clinical studies on two cases suggest that breast tumors can be much more accurately detected by the multimodality method.

Algorithms↗
PubMed2006

Differences in the lesion formation process between focused ultrasound and microwave ablations.

The objective is to understand the differences in the lesion formation processes between microwave and high-intensity focused ultrasound (HIFU) ablation. The lesions formed by microwaves and HIFU were real-time monitored and compared using transparent tissue-mimicking phantoms at 60 and 70 W of driving electrical power. Microwaves and HIFU produced lesions different in shape, size, and developing processes. For HIFU ablations, the hyperechoic region appeared bigger in ultrasonic images, as compared with the protein denatured region observed optically at the end of 100 s ablations. On the contrary, the hyperechoic signal was only limited to a small region along the antenna of a microwave ablator. Careful monitoring and controlling the lesion formation process is essential for successful microwaves and HIFU thermal ablations.

Animals↗
PubMedDate not supplied

Microwave leakage during patient treatment.

In light of the BRH proposed draft standard for microwave leakage of 10 mW/cm2, microwave leakage measurements were taken under two conditions. The first used a microwave tissue equivalent phantom in which leakage cata was accumulated as a function of net forward power and aperture-to-skin distance (SSD). This is similar to the BRH setup. In the second condition, during actual microwave hyperthermia treatments data was accumulated on several patients at different anatomical sites. The results of these experiments show a marked increase of microwave leakage occurring during patient treatment than that which can be predicted from static phantom results.

Humans↗
PubMed2003

Microwave sterilization of femoral head allograft.

The potential shortage of allograft bone has led to the need to investigate other sources of bone for allografts. Some allograft bone donated from primary total hip arthroplasty recipients must be discarded or treated to become usable as a result of bacterial contamination. Femoral head allografts were contaminated with Staphylococcus aureus and Bacillus subtilis. A domestic microwave oven was used. The contaminated bone was exposed to microwave irradiation for different time periods. The samples were then cultured to attempt to grow the two bacterial species. The contaminated bone samples failed to grow any organisms after 2 min of exposure to microwave irradiation. This study shows that sterilization of femoral head allografts contaminated with S. aureus and B. subtilis can be achieved with microwave irradiation in a domestic microwave oven. This method of sterilization of bone allografts is cheap, easily used, and an effective way to process contaminated bone.

Bacillus subtilis↗
PubMed1981

Influence of acute microwave radiation on cardiac function in normal and myocardial ischemic cats.

Exposure of biological specimens to microwave radiation in vivo and in vitro has been reported to cause alterations to the cardiovascular system. In addition, microwave radiation may cause effects in damaged cardiac tissue that are not observed in normal tissue. In this study, we examined the influence of direct microwave irradiation (2.45 GHz, continuous wave) of the intact exposed heart on cardiac function in cats with and without myocardial ischemia. Myocardial ischemia was induced by occlusion of the left anterior descending coronary artery. In the sham-nonexposed and sham-plus-microwave exposed animals the coronary artery was isolated but not occluded. The exposed hearts were either irradiated at a specific absorption rate (SAR) of 30 mW/g or not irradiated, and were monitored for 5 h. At a SAR of 30 mW/g, the temperature of the exposed tissue increased at an initial rate of 0.43 degrees C/min in dead cats. However, in live animals, no increases in aortic blood temperatures occurred during irradiation. Mean arterial blood pressure, cardiac output, heart rate, plasma and myocardial creatine phosphokinase, and S-T segment were not influenced by 5 h of microwave irradiation of the myocardium in cats with or without myocardial ischemia.

Animals↗
PubMed1983

Behavioral and autonomic thermoregulation in mice exposed to microwave radiation.

Preferred ambient temperature (Ta) and breathing rate were measured in free-moving mice exposed to 2,450-MHz microwaves. A waveguide-exposure system was imposed with a longitudinal temperature gradient that permitted mice to select their preferred Ta. Breathing rate was determined by analyzing the rhythmic shifts in microwave energy not absorbed by the animal. Without microwave exposure mice selected an average Ta of 31 degrees C. This preferred Ta did not change until the specific absorption rate (SAR) at 2,450 MHz exceeded approximately 7.0 W X kg-1. Mice maintained their breathing rate near baseline levels by selecting a cooler Ta during microwave exposure. In contrast, mice maintained at 31 degrees C underwent a sharp increase in breathing rate when SAR exceeded approximately 7.0 W X kg-1. Mice exposed to microwaves in a waveguide with a temperature gradient increased breathing rate 0.6 breaths/min per unit increase in SAR, whereas without the temperature gradient breathing rate increased by 9.6 breaths/min per unit increase in SAR. Data from this study support previous studies that have shown behavioral thermoregulation is more effective (or efficient) in minimizing a thermal load than autonomic thermoregulation.

Animals↗
PubMed1989

Acute thermoregulatory responses of the immature rat to warming by low-level 2,450-MHz microwave radiation.

Rats were tested at 6-7 days of age to determine thermoregulatory responses to microwave exposure (2,450-MHz; continuous wave). Each animal was partially restrained in a cylindrical holder and irradiated at a power density of either 5 or 20 mW/cm2 [specific absorption rate = 0.60 (W/kg)/(mW/cm2)] at a cold ambient temperature (Ta). Following a 1-hour thermal equilibration period, each rat was monitored at 1-min intervals during 1-hour microwave exposure and 1-hour recovery periods. Colonic temperature (Tco), determined with a Vitek probe, and metabolic heat production (M), derived from measures of oxygen consumption, were sampled and recorded during these periods. Tco increased significantly above initial level at both power densities and reached a plateau after 45 min of microwave exposure. Tco doubled with a four-fold increase in microwave intensity. Prior to exposure, M was elevated in response to cold Ta and remained unchanged during exposure at 5 mW/cm2, but decreased 7.2 W/kg during exposure at 20 mW/cm2. The results indicate that the hypothermic rat pup can be effectively warmed by low-level microwave irradiation and is capable of altering metabolism in response to such heating.

Animals↗
PubMed1996

Laparoscopic microwave thermotherapy on small renal tumors: experimental studies using implanted VX-2 tumors in rabbits.

OBJECTIVE: To investigate the effectiveness of microwave thermotherapy on implanted renal VX-2 tumors. METHODS: Fifteen rabbits with implanted renal VX-2 tumors were divided into three groups according to the type of therapy: nephrectomy, laparoscopic microwave thermotherapy, and no treatment. Both the anticancer effect and safety were compared among these groups. RESULTS: The survival rate in the laparoscopic microwave thermotherapy group was significantly higher than that in the no-treatment group, and was the same as that in the nephrectomy group. The serum creatinine level did not increase after microwave therapy. CONCLUSION: Laparoscopic microwave thermotherapy may be useful for a nephron-salvaging treatment in small implanted renal VX-2 tumors in rabbits.

Animals↗
PubMed2005

Fixation of soft tissue surrounded by bone with microwave irradiation: electron microscopic observation of guinea pig inner ear.

When electron microscopy is performed on organs such as the inner ear that cannot be removed immediately after decapitation of animals, it is necessary to fix the target organ or tissue by systemic or regional perfusion fixation. However, such methods of fixation can increase vascular pressure or perilymphatic pressure, making it difficult to perform precise morphological observation of the vascular endothelial cells and membranous labyrinth. We recently attempted fixation of the cochlea by microwave irradiation. Guinea pigs were decapitated. The bullas were then removed from each animal and fixed in a mixture of 2% paraformaldehyde and 0.5% glutaraldehyde. Microwave (300 W) irradiation was then applied to the specimen for 1 minute. The fixative was immediately replaced with new fixative (4 degrees C). This sequence of manipulations was repeated 10 times, for a cumulative microwave irradiation time of 10 minutes. During the microwave irradiation period, the fixative temperature was kept at about 30 degrees C. After the last round of irradiation, the specimens were kept immersed in the fixative for 1 hour. After a small slit was created in the bone on the lateral wall of the cochlea, the specimens were post-fixed in osmic acid and embedded in Epon 812. Each specimen was cut into halves along the plane containing the modiolus of the cochlea. After the bone on the lateral wall of the cochlea was cut off under a stereoscopic microscope, ultrathin sections were prepared for observation under a transmission electron microscope. With this technique, the stria vascularis and the organ of Corti were fixed to a degree comparable to or better than that achieved with the conventional method of fixation. Fixation with microwave irradiation is relatively simple and can solve the problems associated with perfusion fixation, and thus provides an excellent means of fixation. This technique appears to be particularly promising for fixation for soft tissue surrounded by bone.

Animals↗